My brother-in-law is convinced they are readily available to the public and the internet is the prime source for purchasing.......he's a dummy.
Hell, since I live in Michigan, I couldn't even purchase an air rifle I wanted over the internet without having to go thru a local FFL dealer....
While full-auto weapons have always been more expensive than semi-autos, due to the "Firearms Owners Protection Act," it was declared that no full-auto weapons manufactured after the act was passed and signed (1985) could be sold to civilians. So the number of full-auto weapons in civilian hands was effectively capped, and the prices have skyrocketed ever since.
Mark